The present invention concerns a machine for working sheet metal.
As is known, machines for working sheet metal essentially comprise a work surface, a work station, and an element for moving the sheet metal on the work surface to and from the work station. The work station comprises an upper turret supporting a plurality of punch tools, a lower turret supporting a plurality of die tools, and a hammer which presses a punch tool towards a corresponding die tool. The machine described above is further provided with a central electronic processing unit which automatically manages the entire processing cycle.
In use, the punching stage involves:
rotating the upper turret to bring the punch tool to be used into alignment with the hammer; PA1 rotating the lower turret to bring the die tool corresponding to the aforesaid punch tool into alignment with the hammer; PA1 securing both turrets to a fixed structure; and controlling the stroke of the hammer. PA1 a work surface on which lies sheet metal; PA1 a fixed structure that supports the said work surface; PA1 a work station provided with a hammer movable along a first vertical axis along which the punching of the said sheet metal is effected; PA1 a plurality of punch units, each having a first holder and a punch tool; PA1 a plurality of die units, each having a second holder and a die tool; PA1 characterized in that it includes a first rotatable table in which the said punch units are stored, which transfers one said punch unit to the said work station, a second rotatable table in which the said die units are stored, which transfers one said die unit to the said work station, and characterized in that the said work station comprises first means for centring the said punch unit with respect to the first vertical axis by securing the said first holder to the said fixed structure, and second means for centering the said die unit with respect to the said first axis by securing the said second holder to the said fixed structure, excluding the said tables from this securing, which tables are therefore not affected by the mechanical stresses generated by the punching, stresses that are transmitted directly from the first and second centering means to the said fixed structure.
The machine described above has several disadvantages. In particular, the turrets are used both for transferring the tools to the work zone and for centering the tools with respect to the work axis of the hammer. In order to transfer the tools, the turrets must be rotatable about a vertical axis and they must be supported by a fixed structure by means of bearings. In order to center the tools, both of the turrets must be joined to the fixed structure and, since the turrets are circular, they must be locked from several radial directions. Furthermore, the turrets must be formed from a highly resilient material and must be appropriately dimensioned as they must withstand the mechanical stresses transmitted from the tools during the punching stage. It is clear that the aforesaid bearings must also be appropriately dimensioned since the mechanical stresses are also transmitted to them during the punching stage.
In short, the fact that the turrets have a dual function (transferring and centering the tools), they must be produced from mechanically valuable materials and be of large dimensions in order to withstand the mechanical stresses, they must be provided with a series of devices to enable the rotation and centering of the tools, and must be subjected to special processing in order to perform the aforesaid functions. Among the special processing to be considered are the seats for the tools, which must be extremely precise, and the shape of the upper surface of the lower turret which acts as the work surface in that the sheet metal to be processed lies on this surface.
It should be emphasized that as the dimensions of the turret increase, the more powerful, and therefore more costly, the means for motorizing the turrets themselves must be. In short, the aforesaid turrets are the elements of the machine on which the greatest and most costly processing must be performed, and these turrets therefore have high production and installation costs. In some machines, in order to protect the lower turret and the elements with which it is provided from wear caused by the aforesaid mechanical stresses, dampening means are installed between this lower turret and the fixed structure, which increases costs and involves further processing of the lower turret.